CVE-2024-42231 in Linux
Summary
by MITRE • 07/30/2024
In the Linux kernel, the following vulnerability has been resolved:
btrfs: zoned: fix calc_available_free_space() for zoned mode
calc_available_free_space() returns the total size of metadata (or system) block groups, which can be allocated from unallocated disk space. The logic is wrong on zoned mode in two places.
First, the calculation of data_chunk_size is wrong. We always allocate one zone as one chunk, and no partial allocation of a zone. So, we should use zone_size (= data_sinfo->chunk_size) as it is.
Second, the result "avail" may not be zone aligned. Since we always allocate one zone as one chunk on zoned mode, returning non-zone size aligned bytes will result in less pressure on the async metadata reclaim process.
This is serious for the nearly full state with a large zone size device. Allowing over-commit too much will result in less async reclaim work and end up in ENOSPC. We can align down to the zone size to avoid that.
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Analysis
by VulDB Data Team • 07/19/2025
The vulnerability identified as CVE-2024-42231 affects the Linux kernel's btrfs filesystem implementation specifically when operating in zoned mode. This issue resides in the calc_available_free_space() function which is responsible for calculating available free space for metadata and system block groups in zoned storage environments. The flaw manifests in two critical areas of the calculation logic that directly impact how space is allocated and managed within zoned storage devices. The btrfs filesystem's zoned mode support is designed to work with host-managed zoned storage devices where the storage is divided into zones that must be managed according to specific allocation rules. When these rules are not properly enforced, the filesystem can misestimate available space and potentially cause allocation failures.
The primary technical flaw occurs in the calculation of data_chunk_size where the implementation incorrectly handles zone allocation boundaries. In zoned mode, the system is designed to allocate entire zones as chunks rather than allowing partial zone allocations, which is a fundamental requirement for maintaining the integrity of zoned storage operations. However, the current implementation fails to properly utilize the zone_size value that represents the actual chunk_size from data_sinfo, instead applying incorrect calculation logic that can lead to miscalculations of available space. This error is particularly problematic because it affects the fundamental space accounting mechanism that determines how much space can be allocated for metadata operations.
The second critical issue involves the alignment of the calculated available space result, which may not conform to zone boundaries. In zoned storage environments, maintaining zone alignment is essential for proper operation since partial zone allocations are not permitted and can cause significant performance degradation or allocation failures. When the function returns space values that are not properly aligned to zone boundaries, it creates inconsistencies in the space management algorithm that can lead to over-commitment of resources. This over-commitment scenario becomes particularly dangerous when dealing with nearly full devices that have large zone sizes, as it can result in the async metadata reclaim process being overwhelmed with less work than necessary, ultimately leading to ENOSPC (No space left on device) errors.
This vulnerability directly impacts the operational stability and reliability of btrfs filesystems running in zoned mode, particularly in high-performance storage environments where proper space management is critical. The issue can cause unexpected allocation failures and system instability when the filesystem encounters nearly full conditions with large zone sizes, potentially leading to complete storage exhaustion scenarios. From a cybersecurity perspective, this vulnerability represents a denial-of-service risk that could be exploited by malicious actors to cause storage system failures or to exhaust available storage space intentionally. The flaw aligns with CWE-129, which addresses improper validation of the length/size of input buffers, and relates to ATT&CK technique T1490, specifically data destruction, as the vulnerability can lead to complete storage exhaustion conditions. The fix requires proper zone size alignment and correct handling of chunk size calculations to ensure that btrfs can properly manage space allocation in zoned storage environments without causing over-commitment issues or ENOSPC errors during critical system operations.